This invention relates to an open-end friction spinning machine having a plurality of spinning units arranged next to one another. Each spinning unit contains two rollers that are arranged next to one another and are drivable in the same rotational direction to form a wedge-shaped gap serving as a yarn forming point or region. Each spinning unit also contains a feeding and opening device for the feeding of individual fibers via a fiber feeding duct to a feeding portion of the wedge-shaped gap, a withdrawal device for withdrawing the spun yarn in the longitudinal direction of the wedge-shaped gap, and a winding device for winding the spun yarn onto a spool. The spinning machine also has a movable servicing apparatus that can be applied to respective spinning units in need of servicing. This servicing apparatus is equipped with devices for receiving the broken yarn end from the spool, with devices for returning the yarn end into the spinning unit in need of servicing, with devices for controlling the feeding of fibers during the piecing process, with devices for withdrawing the pieced yarn, and with devices for winding the pieced yarn onto the spool.
In the case of an individual open-end friction spinning device, it is known from European Published Unexamined Application (EP-OS) No. 34 427 to manually carry out a piecing process. In this case, the winding spool is lifted off its operational drive, after which a spun yarn end is unwound and shortened to a predetermined length. The length of the yarn end is established in such a way that it reaches into the area of the yarn forming point, i.e. into the area of a fiber feeding duct opening in the direction of the wedge-shaped gap. The shortened yarn end must be held at a distance from the wedge-shaped gap in straight stretched condition. Then a suction device that had been switched off for the return of the yarn end is switched on again, this suction device normally affecting the area of the wedge-shaped gap. Almost simultaneously with the switching-on of this suction device, the fiber feeding must be started, after which the yarn withdrawal is resumed by placing the winding spool on its operational drive. The yarn that is led past the operational withdrawal device during the piecing must then be inserted into the withdrawal device. In the case of this piecing process, no high-quality yarn piecings can be obtained which with respect to their appearance and their stability properties correspond substantially to the spun yarn. One of the reasons for the poor quality piecings is that the position of the returned yarn end within the spinning unit is not really controlled. Another reason for the poor quality piecings is that the cut-off yarn end results in a thickened point when the newly fed fibers are deposited, which, in addition, does not have sufficient strength.
The invention is based on the objective of permitting a piecing process that can be carried out automatically, where the yarn end takes up a defined position within the spinning unit and where the yarn end exhibits a configuration that is suitable for piecing.
This objective is achieved according to the invention by providing a twist blocking means for receiving and holding the yarn end returned beyond the feeding point in the area facing away from the withdrawal device of the spinning unit, approximately as an extension of the wedge-shaped gap of the friction rollers, and by providing means for exposing the area of the yarn end located behind the twist blocking means in the yarn withdrawal direction to the frictional effect of the turning friction rollers.
Since the yarn end is returned into the twist blocking means and is held there, it takes up a defined position within the spinning unit according to preferred embodiments of the invention. Since the yarn end following the twist blocking means in the yarn withdrawl direction is subjected to the frictional effect of the turning rollers, it is untwisted in the area between the twist blocking means and the area of the rollers exercising the frictional effect and is freed of its spinning twist. In this area, the cutting or severing of the yarn end will then take place, resulting in a fiberbeard-type end that is suitable for piecing, at which end the fibers fed during the piecing process can deposit and tie up well so that a high-quality yarn piecing is obtained which with respect to strength and appearance is comparable to the remaining spun normally yarn. The severing of the yarn end will take place at a predetermined location in each instance, approximately a staple length of the fibers from the twist blocking means.
In an advantageous development of the invention, it is provided that the distance between the twist blocking means and the area in which the yarn end in the wedge-shaped gap of the rollers is exposed to the frictional effect is at least equal to, and preferably larger, than the fiber staple length. The result is that the cutting of the yarn end takes place without the separating of the individual fibers.
In a further development of certain preferred embodiments of the invention, it is provided that each spinning unit is equipped with a stationary twist blocking means, and that the servicing apparatus is equipped with means for actuating the twist blocking means.
In a further development of certain preferred embodiments of the invention, it is provided that the movable servicing apparatus is provided with a twist blocking means that can be applied to the spinning unit in need of servicing in the area facing away from the withdrawal device as an extension of the wedge-shaped gap of the rollers of the spinning unit. This development results in a simplification because of the fact that, on the one hand, the twist blocking means must exist only once, namely at the servicing apparatus, and on the other hand, the means for actuating and controlling the twist blocking means must also only exist once. It is advantageous in this case that the twist blocking means aligns itsef at a stop or similar device of the spinning unit so that precisely defined identical conditions exist at each spinning unit during the piecing.
In a further development of certain preferred embodiments of the invention, it is provided that the twist blocking means contains a suction pipe that is connected to a vacuum source. This makes is possible to return the yarn end into the twist blocking means with a sufficient length that does not have to be exactly defined. In addition, the part of the yarn end that is detached during the cutting can be transported in a simple manner out of the area of the spinning unit.
In a further development of certain preferred embodiments of the invention, a yarn clamp is provided as the twist blocking means. As compared to other possibilities of making a twist blocking means, this yarn clamp has the advantage that, irrespective of outside conditions, the same conditions always exist, and especially, that it is prevented that the yarn can shift in longitudinal direction so that the cutting takes place practically at the same point in all cases.
In a further development of the invention, it is provided that the twist blocking means is displaced in the direction away from the rollers with respect to the wedge-shaped gap. The result is that the cutting or severing of the yarn end takes place in an area that is not yet in contact with the shell or friction surfaces of the rollers. The separated yarn end that is opened up to form a fiberbeard reaches the area of the wedge-shaped gap only at the time of the withdrawal for the piecing process. Thus it is prevented that the end twisted open to form a fiberbeard is twisted together before the actual piecing process.
In a further development of certain preferred embodiments of the invention, it is provided that the servicing apparatus is equipped with means for interrupting and switching-on the operational drive of the rollers of the spinning unit to be serviced, and with an auxiliary drive that can be applied to the rollers. In a further development of certain preferred embodiments of the invention, it is provided that each spinning unit is equipped with a suction device acting in the area of the wedge-shaped gap, and that the servicing apparatus is equipped with means for controlling the effect of the suction device of the spinning unit to be serviced. As a result it is possible to control all devices required for the piecing process directly from the servicing apparatus so that exactly the same conditions can be created for each piecing process.
In a further development of certain preferred embodiments of the invention it is provided that the devices for the rewithdrawal of the pieced yarn, the devices for the winding of the yarn, the devices for controlling the feeding of the fibers and the auxiliary drive for the rollers contain driving motors with controllable speed and are connected to a control circuit controlling the coordination of the speeds with respect to one another. As a result, it is possible to directly coordinate and proportion the individual work steps in a piecing process with respect to one another. In addition, it is possible to let the piecing process take place at reduced speeds which are adjustable in such a way that during the piecing a yarn count is spun that corresponds to the operationally spun yarn count. It is also possible after the piecing to increase the speeds to the operational speeds in such a way that also during this time the desired yarn count is spun. This is advantageous because of the high delivery speeds of the spinning units of an open-end friction spinning machine because already during the piecing and the increasing to operational speeds, relatively large quantities of yarn are produced which reach the spool to be furether processed. Further objects, features, and advantages of the present invention will become more apparent from the following description when taken with the accompanying drawings which show, for purposes of illustration only, several embodiments in accordance with the present invention.